Process for the production of a multicoat finish, and an aqueous paint

ABSTRACT

The invention relates to a process for the production of a multicoat finish, in which an aqueous basecoat is used which contains as binder a polymer which can be obtained by polymerizing in an organic solvent 
     (A) ethylenically unsaturated monomers in the presence of 
     (B) a polyurethane resin containing polymerizable double bonds 
     and converting the resultant reaction product to an aqueous dispersion.

The invention relates to a process in which

(1) a pigmented aqueous basecoat is applied to the substrate surface,

(2) a polymer film is formed from the composition applied in stage (1),

(3) a transparent topcoat is applied to the basecoat obtained in thisway and subsequently

(4) the basecoat is baked together with the topcoat.

The invention also relates to an aqueous paint.

The process for the production of multicoat finishes described above isknown and is employed especially for the finishing of automobile bodies.

The result of the process described above crucially depends on thebasecoat used. The basecoat has a strong influence on the quality of theoverall finish.

No aqueous basecoats have been known up to now which are suitable forproduction line finishing and for refinishing and which furnishhigh-quality overall finishes.

The object of the present invention consists in providing novel aqueouspaints which are suitable as basecoats for performing the processdescribed above.

This object is achieved by making available aqueous paints whichcomprise as binder a polymer which can be obtained by polymerizing in anorganic solvent or in a mixture of organic solvents

(A) ethylenically unsaturated monomers or a mixture of ethylenicallyunsaturated monomers in the presence of

(B) a polyurethane resin which has a number average molecular weight of200 to 30,000, preferably of 1,000 to 5,000 and contains on statisticalaverage 0.05 to 1.1, preferably 0.2 to 0.9, particularly preferably 0.3to 0.7 polymerizable double bonds per molecule

and converting the reaction product obtained in this way to an aqueousdispersion.

The basecoats according to the invention are distinguished by the factthat they may be recoated after a short time with an aqueous orconventional clearcoat by the "wet-on-wet" process without disturbingthe basecoat film, and that they furnish--even at low bakingtemperatures, for example at 80° C.--finishes with high moistureresistance and good mechanical properties.

EP-A-297,576 discloses basecoats which are suitable for performing theprocess under discussion. The basecoats described in EP-A-297,576comprise as binders polymers which can be obtained by polymerizing inwater ethylenically unsaturated compounds in the presence of apolyurethane resin which is free from double bonds. This process iscostly and gives rise to binder dispersions which often contain acoagulate and are unsuitable for pigment dispersion. In addition, thebinders disclosed in EP-A-297,576 differ significantly in their chemicalstructure from the binders used according to the invention.

For the preparation of the binders used according to the invention apolyurethane resin (B) is prepared in a first step according towell-known methods of polyurethane chemistry. The polyurethane resin isprepared from the following components:

(a) a polyester polyol and/or a polyether polyol having a number averagemolecular weight of 400 to 5,000, or a mixture of such polyester polyolsand/or polyether polyols,

(b) a polyisocyanate or a mixture of polyisocyanates,

(c) if appropriate, a compound which contains in addition to apolymerizable double bond at least one group reactive toward NCO groups,or a mixture of such compounds,

(d) if appropriate, a compound which contains in the molecule at leastone group which is reactive toward isocyanate groups and at least onegroup which is capable of forming anions, or a mixture of suchcompounds,

(e) if appropriate, a compound which contains in the molecule at leastone group which is reactive toward NCO groups and at least onepoly(oxyalkylene) group, or a mixture of such compounds and, ifappropriate,

(f) an organic compound containing hydroxyl and/or amino groups having amolecular weight of 60 to 600, or a mixture of such compounds.

The polyurethane resin (B) should have a number average molecular weightof 200 to 30,000, preferably 1,000 to 5,000, and on statistical average0.05 to 1.1, preferably 0.2 to 0.9, particularly preferably 0.3 to 0.7polymerizable double bonds per molecule. It is preferred that thepolyurethane resin (B) has an acid value of 0 to 2.0. As is known to aperson skilled in the art, the molecular weight of the polyurethaneresins can be controlled in particular by the quantity ratio and thefunctionality of the starting compounds (a) to (f) used.

The polyurethane resins may be prepared both in bulk and in organicsolvents.

The polyurethane resins may be prepared by simultaneous reaction of allstarting compounds. However, in many cases it is expedient to preparethe polyurethane resins in stages. Thus, for example, it is possible toprepare a prepolymer containing isocyanate groups from the components(a) and (b) which is then reacted further with the component (c) . It isfurther possible to prepare from the components (a), (b), (c) and, ifappropriate, (d) and (e) a prepolymer containing isocyanate groups whichcan subsequently be reacted with the component (f) to formhigh-molecular polyurethanes. In those cases in which a compound is usedas the component (c) which only contains a single group reactive towardisocyanate groups, it is-possible to prepare in a first stage from (b)and (c) an intermediate containing isocyanate groups which can besubsequently further reacted with the other components.

The reaction of the components (a) to (f) is expediently carried out inthe presence of catalysts such as, for example, dibutyltin dilaurate,dibutyltin maleate, tertiary amines etc.

The amounts of the component (a), (b), (c), (d), (e) and (f) to be usedare determined by the targeted number average molecular weight and thetargeted acid value. The polymerizable double bonds can be introducedinto the polyurethane molecules by using components (a) containingpolymerizable double bonds and/or the component (c). It is preferred tointroduce the polymerizable double bonds via component (c).

Saturated and unsaturated polyester polyols and/or polyether polyols, inparticular polyester diols and/or polyether diols, having a numberaverage molecular weight of 400 to 5,000 may be used as the component(a). Examples of suitable polyether diols are polyether diols of thegeneral formula H(--O--(CHR¹)_(n) --)_(m) OH, in which R¹ is hydrogen ora lower, unsubstituted or substituted alkyl radical, n is 2 to 6,preferably 3 to 4 and m is 2 to 100, preferably 5 to 50. Examples arelinear or branched polyether diols such as poly(oxyethylene) glycols,poly(oxypropylene) glycols and poly(oxybutylene) glycols. The chosenpolyether diols should not introduce excessive amounts of ether groups,since otherwise the polymers formed swell in water. The preferredpolyether diols are poly(oxypropylene) glycols in the molecular massrange M_(n) of 400 to 3,000.

Polyester diols are prepared by esterification of organic dicarboxylicacids or their anhydrides with organic diols or they are derived from ahydroxycarboxylic acid or a lactone. To prepare branched polyesterpolyols it is possible to a small extent to use polyols orpolycarboxylic acid of higher valency. The dicarboxylic acids and diolsmay be linear or branched aliphatic, cycloaliphatic or aromaticdicarboxylic acids or diols.

The diols used for the preparation of the polyesters consist, forexample, of alkylene glycols such as ethylene glycol, propylene glycol,butylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol andother diols such as dimethylolcyclohexane. However, small amounts ofpolyols, such as trimethylolpropane, glycerol and pentaerythritol, mayalso be added. The acid component of the polyester consists primarily oflow-molecular dicarboxylic acids or their anhydrides having 2 to 44,preferably 4 to 36 carbon atoms in the molecule. Examples of suitableacids are o-phthalic acid, isophthalic acid, terephthalic acid,tetrahydrophthalic acid, cyclohexanedicarboxylic acid, succinic acid,adipic acid, azelaic acid, sebacic acid, maleic acid, fumaric acid,glutark acid, hexachloroheptanedicarboxylic acid, tetrachlorophthalicacid and/or dimerized fatty acids. Instead of these acids it is alsopossible to use their anhydrides, where they exist. In the synthesis ofpolyester polyols smaller amounts of carboxylic acids with 3 or morecarboxyl groups, for example trimellitic anhydride or the adduct ofmaleic anhydride and unsaturated fatty acids [sic], may also be present.

It is also possible to use polyester diols which are obtained byreacting a lactone with a diol. They are distinguished by the presenceof terminal hydroxyl groups and recurrent polyester moieties of theformula (--CO--(CHR²)_(n) --CH₂ --O). In this formula n is preferably 4to 6 and of the substituent R² is hydrogen, an alkyl, cycloalkyl oralkoxy radical. No substituent contains more than 12 carbon atoms. Thetotal number of carbon atoms in the substituent does not exceed 12 perlactone ring. Corresponding examples are hydroxycaproic acid,hydroxybutyric acid, hydroxydecanoic acid and/or hydroxystearic acid.

The unsubstituted ε-caprolactone in which n has the value of 4 and eachof the R² substituents is hydrogen, is preferred for the preparation ofthe polyester diols. The reaction with the lactone is initiated bylow-molecular polyols such as ethylene glycol, 1,3-propanediol,1,4-butanediol and dimethylolcyclohexane. However, other reactioncomponents, such as ethylenediamine, alkyldialkanolamines or even ureamay also be reacted with caprolactone. Suitable high-molecular diols arealso polylactam diols which are prepared by reaction of, for example,ε-caprolactam with low-molecular diols.

If polymerizable double bonds are to be introduced into the polyurethanemolecules via the component (a), then the components (a) used mustcontain polymerizable double bonds. Examples of such components (a) arepolyester polyols, preferably polyester diols, which have been preparedby using polyols and/or polycarboxylic acids containing polymerizabledouble bonds. Examples of polyols containing polymerizable double bondsare: trimethylolpropane monoallyl ether, glycerol monoallyl ether,pentaerythritol monoallyl ether and pentaerythritol diallyl ether.Examples of carboxylic acids containing polymerizable double bonds arealkenedicarboxylic acids, maleic acid and unsaturated dimerized fattyacids.

Aliphatic and/or cycloaliphatic and/or aromatic polyisocyanates may beused as the component (b). Examples of aromatic polyisocyanates arephenylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate,biphenylene diisocyanate, naphthylene diisocyanate and diphenylmethanediisocyanate.

On account of their good resistance to ultraviolet light (cyclo)aliphatic polyisocyanates furnish products having low tendency toyellowing. Examples of cycloaliphatic polyisocyanates are isophoronediisocyanate, cyclopentylene diisocyanate and the hydrogenation productsof aromatic diisocyanates such as cyclohexylene diisocyanate,methylcyclohexylene diisocyanate and dicyclohexylmethane diisocyanate.Aliphatic diisocyanates are compounds of the formula

    OCN--(CR.sup.3.sub.2)r--NCO [sic],

in which r is an integer from 2 to 20, in particular from 6 to 8, and R³which can be the same or different, is hydrogen or a low alkyl radicalhaving 1 to 8 carbon atoms, preferably 1 or 2 carbon atoms.Corresponding examples are trimethylene diisocyanate, tetramethylenediisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate,propylene diisocyanate, ethylethylene diisocyanate, dimethylethyldiisocyanate, methyl trimethylene diisocyanate and trimethylhexanediisocyanate. A further example of an aliphatic diisocyanate istetramethylxylene diisocyanate. Isophorone diisocyanate anddicyclohexylmethane diisocyanate are particularly preferred as thediisocyanates.

The composition of the component (b) must in respect of functionality ofthe polyisocyanates be such that it contains no crosslinked polyurethaneresin. In addition to diisocyanates, the component (b) may also containa proportion of polyisocyanates having functionalities greater than two,for example triisocyanates.

Products which are formed by trimerization or oligomerization ofdiisocyanates or by reaction of diisocyanates with compounds containingpolyfunctional OH or NH groups, have been found satisfactory as thetriisocyanates. This group of compounds includes, for example, thebiuret of hexamethylene diisocyanate and water, the isocyanurate ofhexamethylene diisocyanate or the adduct of isophorone diisocyanate andtrimethylolpropane. The average functionality can be reduced, ifdesired, by the addition of monoisocyanates. Examples of suchchain-terminating monoisocyanates are phenyl isocyanate, cyclohexylisocyanate and stearyl isocyanate.

The component (c) serves for the introduction of polymerizable doublebonds into the polyurethane resin molecules. It is preferred to use asthe component (c) a compound which contains at least two groups reactivetoward NCO groups and a polymerizable double bond. Compounds whichcontain two groups reactive toward NCO groups in addition to apolymerizable double bond are used particularly preferably as thecomponent (c). Examples of groups reactive toward NCO groups are --OH,--SH, >NH and --NH₂ groups, --OH, >NH and --NH₂ groups being preferred.Examples of compounds which can be used as the component (c) are:hydroxy (meth) acrylates, in particular hydroxyalkyl (meth)acrylatessuch as hydroxyethyl, hydroxypropyl, hydroxybutyl or hydroxyhexyl(meth)acrylate and 2,3-dihydroxypropyl (meth) acrylate,2,3-dihydroxypropyl monoallyl ether, allyl 2,3-dihydroxypropanoate,glycerol mono(meth)acrylate, glycerol monoallyl ether, pentaerythritolmono(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritolmonoallyl ether, pentaerythritol diallyl ether, trimethylolpropanemonoallyl ether, trimethylpropane [sic] mono(meth)acrylate andtrimethylolpropane diallyl ether. Trimethylolpropane monoallyl ether,glycerol mono(meth)acrylate, pentaerythritol di(meth)acrylate,pentaerythritol diallyl ether, glycerol monoallyl ether andtrimethylolpropane mono(meth)acrylate are preferably used as thecomponent (c). Trimethylolpropane monoallyl ether, glycerol monoallylether and allyl 2,3-dihydroxypropanoate are used particularly preferablyas the component (c). It is preferred to incorporate the components (c)which contain at least two groups reactive toward NCO groups into thepolyurethane molecules as part of a chain (not terminal).

The introduction of groups capable of forming anions into thepolyurethane molecules is carried out by incorporating in thepolyurethane molecules compounds (d) which contain in the molecule atleast one group reactive toward isocyanate groups and a group capable offorming anions.

The Mount of the component (d) to be used can be calculated from thetargeted acid value.

Compounds which contain in the molecule two groups reactive towardisocyanate groups are preferably used as the component (d). Suitablegroups reactive toward isocyanate groups are in particular hydroxylgroups as well as primary and/or secondary amino groups. Suitable groupscapable of forming anions are carboxyl, sulfonic acid and/or phosphonicacid groups, carboxyl groups being preferred. Alkanoic acids having twosubstituents on the e carbon atom may be used, for example, as thecomponent (d). The substituent may be a hydroxyl group, an alkyl groupor, preferably, an alkylol group. These alkanoic acids have at leastone, generally 1 to 3 carboxyl groups in the molecule. They have two toabout 25, preferably 3 to 10 carbon atoms. Examples of the component (b)are dihydroxypropionic acid, dihydroxysuccinic acid and dihydroxybenzoicacid. A group of alkanoic acids which is particularly preferred are theα,α-dimethylolalkanoic acids of the general formula R⁴ --C(CH₂ OH)₂COOH, in which R⁴ is a hydrogen atom or an alkyl group having up toabout 20 carbon atoms.

Examples of such compounds are 2,2-dimethylolacetic acid,2,2-dimethylolpropionic acid, 2,2-dimethylolbutyric acid and2,2-dimethylolpentanoic acid. 2,2-Dimethylolpropionic acid is thepreferred dihydroxyalkanoic acid. Examples of compounds containing aminogroups are α,δ-diaminovaleric acid, 3,4-diaminobenzoic acid,2,4-diaminotoluenesulfonic acid and 2,4-diaminodiphenyl ether sulfonicacid.

Poly(oxyalkylene) groups can be introduced into the polyurethanemolecules as non-ionic stabilizing groups with the aid of the component(e). Alkoxypoly(oxyalkylene) alcohols of the general formula R'O--(--CH₂--CHR'--O--)_(n) H in which R' is an alkyl radical of 1 to 6 carbonatoms, R' is a hydrogen atom or an alkyl radical of 1 to 6 carbon atomsand n is a number between 20 and 75 may be used, for example, as thecomponent (e) .

The use of the component (f) leads to a molecular weight increase of thepolyurethane resins. Polyols having up to 36 carbon atoms per molecule,such as ethylene glycol, diethylene glycol, triethylene glycol,1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butylene glycol,1,6-hexanediol, trimethylolpropane, castor oil or hydrogenated castoroil, di(trimethylolpropane) ether, pentaerythritol, 1,2-cyclohexanediol,1,4-cyclohexanedimethanol, bisphenol A, bisphenol F, neopentyl glycol,neopentyl glycol hydroxypivalate, hydroxyethylated or hydroxypropylatedbisphenol A, hydrogenated bisphenol A and mixtures thereof may be used,for example, as the component (f). The polyols are generally used inamounts of up to 30% by weight, preferably of 2 to 20% by weight, basedon the amount of the component (a) and(f) used.

Diamines and/or polyamines with primary and/or secondary amino groupsmay also be used as the component (f). Polyamines are essentiallyalkylene polyamines having 1 to 40 carbon atoms, preferably about 2 to15 carbon atoms. They may contain substituents which have no hydrogenatoms reactive with isocyanate groups. Examples are polyamines withlinear or branched aliphatic, cycloaliphatic or aromatic structure andat least two primary amino groups. Suitable diamines are hydrazine,ethylenediamine, propylenediamine, 1,4-butylenediamine, piperazine,1,4-cyclohexyldimethylamine, 1,6-hexamethylenediamine,trimethylhexamethylenediamine, menthanediamine, isophoronediamine,4,4'-diaminodicyclohexylmethane and aminoethylethanolamine. Preferreddiamines are hydrazine, alkyldiamines or cycloalkyldiamines such aspropylenediamine and 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane.Polyamines which contain more than two amino groups in the molecule mayalso be used as the component (f). However, in such cases care must betaken--for example by using monoamines at the same time--that nocrosslinked polyurethane resins are obtained. Such usable polyamines arediethylenetriamine, triethylenetetramine, dipropylenediamine anddibutylenetriamine. A suitable example of a monoamine isethylhexylamine.

The binders used according to the invention are prepared by preparing asolution of the polyurethane resin (B) in an organic solvent or amixture of organic solvents and polymerizing in this solutionethylenically unsaturated monomers or a mixture of ethylenicallyunsaturated monomers in a free-radical polymerization and converting theresultant reaction product to an aqueous dispersion. It is preferred touse water-miscible organic solvents. Examples of usable solvents arebutyl glycol, 2-methoxypropanol, n-butanol, methoxybutanol, n-propanol,ethylene glycol monomethyl ether, ethylene glycol monoethyl ether,ethylene glycol monobutyl ether, diethylene glycol monomethyl ether,diethylene glycol monoethyl ether, diethylene glycol diethyl ether,diethylene glycol monobutyl ether and 3-methyl-3-methoxybutanol ormixtures of these solvents.

Ketones, such as acetone, methyl ethyl ketone, diethyl ketone and methylisobutyl ketone, are preferred.

The free-radical polymerization is carried out at temperatures of 80° to160° C., preferably of 100° to 160° C., in the above organic solvents orsolvent mixtures.

Examples of usable polymerization initiators are free radical-forminginitiators, such as benzoyl peroxide, azobisisobutyronitrile and t-butylperbenzoate.

In the polymerization grafting reactions also occur between thepolyurethane resin (B) and the component (A). The components (A) and (B)are used in a weight ratio of 1:10 to 10:1, preferably 1:2 to 2:1,particularly preferably 1:1.

Practically any free-radically polymerizable monomer may be used as theethylenically unsaturated monomer, the usual copolymerizationconstraints which are defined by the Q and e scheme according to Alfreyand Price or by the copolymerization parameters being, however, valid(cf. for example Brandrup and Immergut, Polymer Handbook, 2nd ed. JohnWiley+Sons, New York (1975)). The following can be used as ethylenicallyunsaturated monomers:

(i) aliphatic or cycloaliphatic esters of acrylic acid or methacrylicacid or a mixture of such esters and

(ii) ethylenically unsaturated monomers containing at least one hydroxylgroup in the molecule or a mixture of such monomers and

(iii) ethylenically unsaturated monomers containing at least onecarboxyl group in the molecule or a mixture of such monomers and

(iv) other ethylenically unsaturated monomers which are different from(i), (ii) and (iii) or a mixture of such monomers and

(v) polyunsaturated monomers, in particular ethylenicallypolyunsaturated monomers.

The above monomers are preferably used as mixtures, the component (i)being used in an amount of 0 to 100, preferably of 60 to 90% by weight,the component (ii) in an amount of 0 to 20, preferably of 3 to 12% byweight, the component (iii) in an amount of 0 to 30, preferably of 5 to15% by weight, the component (iv) in an amount of 0 to 30, preferably of0 to 10% by weight and the component (v) in an amount of 0 to 5,preferably of 0% by weight, the sum of the proportions by weight of (i),(ii), (iii), (iv) and (v) always being 100% by weight.

The following can be used, for example, as the component (i): cyclohexylacrylate, cyclohexyl methacrylate, alkyl acrylates and alkylmethacrylates having up to 20 carbon atoms in the alkyl radical, forexample methyl, ethyl, propyl, butyl, hexyl, ethylhexyl, stearyl andlauryl acrylate and methacrylate or mixtures of these monomers.

The following may be used, for example, as the component (ii):hydroxyalkyl acrylates, hydroxyalkyl methacrylates or hydroxyalkylesters of another α,β-ethylenically unsaturated carboxylic acid. Theseesters may be derived from an alkylene glycol which is esterified withthe acid, or they can be obtained by reacting the acid with an alkyleneoxide. Hydroxyalkyl acrylates and hydroxyalkyl methacrylates in whichthe hydroxyalkyl group contains up to 4 carbon atoms, or mixtures ofthese hydroxyalkyl esters, are preferably used as the component (ii).Examples of such hydroxyalkyl esters are 2-hydroxyethyl acrylate,2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropylacrylate, 3-hydroxypropyl methacrylate, 2-hydroxyethyl methacrylate,3-hydroxybutyl acrylate or 4-hydroxybutyl (meth)acrylate. Correspondingesters of other unsaturated acids, for example ethacrylic acid, crotonicacid and similar acids having up to about 6 carbon atoms per molecule,may also be used.

Acrylic acid and/or methacrylic acid are preferably used as thecomponent (iii). However, other ethylenically unsaturated acids havingup to 6 carbon atoms in the molecule may also be used. Examples of suchacids are ethacrylic acid, crotonic acid, maleic acid, fumaric acid andiraconic acid.

The following may be used, for example, as the component (iv):vinylaromatic hydrocarbons such as styrene, α-alkylstyrene andvinyltoluene, acrylamide and methacrylamide, acrylonitrile andmethacrylonitrile or mixtures of these monomers.

Compounds which contain at least two free-radically polymerizable doublebonds in the molecule may be used as the component (v). Examples ofthese are: divinylbenzene, p-methyldivinylbenzene,o-nonyldivinylbenzene, ethanediol di(meth)acrylate, 1,4-butanedioldi(meth) acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolpropanetri(meth)acrylate, pentaerythritol di(meth)acrylate, allyl methacrylate,diallyl phthalate, butanediol divinyl ether, divinylethyleneurea,divinylpropyleneurea, diallyl maleate etc.

The use of difunctional unsaturated monomers such as butanedioldiacrylate or hexanediol diacrylate is preferred. When glycidylmethacrylate and methacrylic acid are used, the corresponding glyceroldimethacrylate forms automatically in the polymerization. The type andamount of polyunsaturated monomers must be carefully adjusted to suitthe reaction conditions (catalysts, reaction temperature, solvents) inorder to avoid gelling. The purpose of the amount of polyunsaturatedmonomers added is to raise the average molecular mass without gelformation. It is preferred, however, not to use any polyunsaturatedmonomers.

The polymers prepared from (A) and (B) and used according to theinvention must contain groups capable of forming anions which areneutralized before or during the transfer of the polymers from theorganic solvent or solvent mixture into water and which allow theformation of stable aqueous dispersions. In addition to the groupscapable of forming anions, the polymers under discussion may alsocontain non-ionic stabilizing groups such as poly(oxyalkylene) groups,in particular poly(oxyethylene) and/or poly(oxypropylene) and/orpoly(oxyethylene) (oxypropylene) groups.

The amount of groups capable of forming anions contained in the polymersprepared from (A) and (B) used according to the invention should be suchthat the polymers have an acid value of 5 to 200, preferably 10 to 40,particularly preferably 15 to 30. The introduction of groups capable offorming anions into the polymers under discussion can be carried out,for example, via the components (d) and (iii). The groups capable offorming anions may be contained exclusively in the component (A) orexclusively in the component (B) or both in the component (A) and thecomponent (B). It is preferred that 50 to 100, preferably 70 to 100,particularly preferably 100% of the groups capable of forming anions arecontained in the component (A).

The introduction of poly(oxyalkylene) groups into the polymers accordingto the invention may be carried out via the component (e) or viaethylenically unsaturated monomers which contain at least onepoly(oxyalkylene) group (for example poly(oxyethylene) (meth)acrylates).The polymers according to the invention should not contain excessiveamounts of poly(oxyalkylene) groups, since otherwise the humidityresistance of the paint films can be reduced. The content ofpoly(oxyalkylene) groups may lie in the proximity of 1 to 10% by weight,preferably 1 to 5% by weight (based on the weight of the polymersprepared from (A) and (B)).

The polymers prepared from (A) and (B) used according to the inventionshould preferably not contain any non-ionic stabilizing groups.

The polymers prepared from (A) and (B) should preferably have a hydroxylvalue of 0 to 100, particularly preferably of 20 to 80. The numberaverage molecular weight of the polymers should preferably be 2,000 to20,000, particularly preferably 5,000 to 12,000.

The polymers which are particularly preferred are those polymersprepared from (A) and (B) which have a polymolecularity index Q of 5 to90, preferably of 10 to 0. The polymolecularity index is the quotientMw:Mn, where M_(w) is the weight average molecular weight and M_(n) isthe number average molecular weight.

The polymolecularity index can be influenced, for example by a targeteduse of regulators and by the type of the solvents used. In addition Q isinfluenced by the content of polymerizable double bonds contained in thecomponent (B). The greater is Q, the smaller is the amount of regulatorused and the amount of solvents used, which can function as regulator.The lower the content of polymerizable double bonds in the component(B), the greater is Q.

Q can be determined by gel permeation chromatography using a polystyrenestandard.

At the end of the polymerization of the component (A) the resultantpolymer is at least partially neutralized and dispersed in water.

Both organic bases and inorganic bases, such as ammonia and hydrazine,may be used for the neutralization. Primary, secondary and tertiaryamines, for example ethylamine, propylamine, dimethylamine,dibutylamine, cyclohexylamine, benzylamine, morpholine, piperidine andtriethanolamine, are preferably used. Tertiary amines, in particulardimethylethanolamine, triethylamine, tripropylamine and tributylamine,are used particularly preferably as the neutralization agent.

If desired, some or preferably all of the organic solvents can bedistilled off from the resultant aqueous binder dispersions. The binderdispersions contain polymer particles whose average particle size isbetween 10 and 500 nm, preferably between 60 to [sic] 150 nm (method ofmeasurement: laser light scatter; measuring instrument: MalvernAutosizer 2 C).

Aqueous paints, in particular aqueous solid-color and aqueous metallicbasecoats can be prepared from the binder dispersions under discussionby generally well known methods. The basecoats may also be used forrefinishing and can be recoated with both aqueous and conventionalclearcoats and powder paints.

In addition to the binders according to the invention, the basecoats maycontain further compatible water-thinnable synthetic resins, for exampleamino resins, polyurethane resins, polyacrylate resins, polyesters andpolyethers.

The basecoats contain preferably 5 to 90, particularly preferably 40 to70% by weight of the binder according to the invention, the percentagesby weight being based on the total solids content of the basecoats.

The basecoats according to the invention may contain as pigmentschromophoric inorganic pigments, for example titanium dioxide, ironoxide, carbon black etc., chromophoric organic pigments and conventionalmetallic pigments (for example commercial aluminum bronzes, stainlesssteel bronzes etc.) and non-metallic effect pigments (for examplepearlescent or interference pigments). The degree of pigmentation is inthe conventional range. It is a particular advantage of the binders usedaccording to the invention that they may also be used as grinding resinand furnish highly stable pigment pastes.

The basecoats according to the invention may further contain crosslinkedpolymeric microparticles, such as those disclosed, for example, inEP-A-38,127, and/or customary inorganic or organic additives. Examplesused as thickener are water-soluble cellulose ethers, such ashydroxyethylcellulose, methylcellulose or carboxymethylcellulose as wellas synthetic polymers containing ionic and/or associatively actinggroups, such as polyvinyl alcohol, poly(meth)acrylamide,poly(meth)acrylic acid, polyvinylpyrrolidone, styrene-maleic anhydrideor ethylene-maleic anhydride copolymers and their derivatives as well ashydrophobically modified ethoxylated urethanes or polyacrylates andpolyacrylate copolymers containing carboxyl groups, having an acid valueof 60 to 780, preferably 200 to 500.

The basecoats according to the invention generally have a solids contentof about 15 to 50% by weight. The solids content varies according to theintended application of the coating compositions. For metallic paints itis, for example, preferably 17 to 25% by weight. For solid-color paintsit is higher, for example 30 to 45% by weight. The paints according tothe invention may additionally contain conventional organic solvents.The content of these should be kept as low as possible. For example, itis below 15% by weight.

The pH of the basecoats according to the invention is generally adjustedto between 6.5 and 9.0. The pH may be adjusted using customary amines,for example ammonia, triethylamine, dimethylaminoethanol andN-methylmorpholine.

The basecoats according to the invention may be recoated with aqueousconventional clearcoats or powder clearcoats.

The object identified at the outset is achieved by the provision of thebasecoats according to the invention.

High-quality finishes may be obtained with the basecoats according tothe invention even without recoating with a transparent topcoat. Theone-coat finishes obtained in this way are particularly distinguished byhigh gloss, good mechanical-technological properties and high humidityresistance.

The aqueous paints according to the invention may be applied to anysubstrate, for example metal, wood, plastics or paper. The applicationmay be performed directly, as is customary in the automotive industry,after an electrodeposition primer and a body filler have been applied.

The paints according to the invention may be applied by spraying,blade-coating, dipping, rolling and preferably by electrostatic andcompressed-air spraying.

The invention is explained in greater detail in the examples below. Allpercentages and parts are by weight, unless expressly stated otherwise.

1. Preparation of Binder Dispersions According to the Invention 1.1Binder Dispersion A

275 g of isophorone diisocyanate are added to a mixture of 336 g of apolyester having a number average molecular weight of 630 based onadipic acid, hexanediol and neopentyl glycol (molar ratio 1:0.5:1), 31 gof neopentyl glycol, 27.8 g of trimethylolpropane monoallyl ether, 0.45g of dibutyltin dilaurate and 279.7 g of methyl ethyl ketone, containedin a 5 1 reaction vessel fitted with a stirrer, a reflux condenser andtwo feed vessels. The reaction mixture is then heated to a temperatureof 80° C. in an atmosphere of nitrogen. When the NCO content reaches2.2%, 66.7 g of trimethylolpropane are added to the reaction mixture andthe reaction is allowed to continue until no more isocyanate groups canbe detected. 248.9 g of methyl ethyl ketone are then added.

A mixture of 312.5 g of n-butyl acrylate, 312.5 g of methylmethacrylate, 74.7 g of hydroxypropyl methacrylate and 58.4 g of acrylicacid is then added to the reaction mixture over 3 hours at a temperatureof 82° C. At the same time 175 g of a 13 percent solution of 2,2'-azobis(methylbutyronitrile) in methyl ethyl ketone are metered in over 3.5hours.

After a further 2.5 hours at 82° C. 56.9 g of dimethylethanolamine and2242 g of deionized water are added.

After removal of the methyl ethyl ketone in vacuo a 40 percent aqueousdispersion which is free from coagulate and has a pH of 8.1 and anaverage particle diameter of 100 mm is obtained.

1.2 Binder Dispersion B

289.5 g of isophorone diisocyanate are added to a mixture of 353.5 g ofa polyester having a number average molecular weight of 630 based onadipic acid, maleic anhydride, hexanediol and ethylbutyl-1,3-propanediol(molar ratio 0.9:0.1:0.5:1), 39.4 g of neopentyl glycol, 18.0 g oftrimethylolpropane monoallyl ether, 0.45 g of dibutyltin dilaurate and330 g of methyl isobutyl ketone, contained in a 5 1 reaction vesselfitted with a stirrer, a reflux condenser and two feed vessels. Thereaction mixture is then heated to a temperature of 105° C. in anatmosphere of nitrogen. When the NCO content reaches 2.2%, 69.6 g oftrimethylolpropane are added to the reaction mixture. When the residualNCO content is less than 0.05%, 150.2 g of methyl isobutyl ketone areadded.

A mixture of 417.4 g of n-butyl acrylate, 217.4 g of methylmethacrylate, 75.9 g of hydroxypropyl methacrylate and 59.4 g of acrylicacid are then added to the reaction mixture over 3 hours at atemperature of 105° C. At the same time 179.9 g of an 11.7 percentsolution of tertiary-butyl perethylhexanoate in methyl isobutyl ketoneare metered in over 3.5 hours.

After a further 2.5 hours at 105° C. 51.3 g of dimethylethanolamine and2310 g of deionized water are added.

After removal of the methyl isobutyl ketone in vacuo a 43 percentaqueous dispersion which is free from coagulate and has a pH of 7.9 andan average particle diameter of 100 run is obtained.

1.3 Binder Dispersion C

285.4 g of isophorone diisocyanate are added to a mixture of 348.8 g ofa polyester having a number average molecular weight of 630 based onadipic acid, hexanediol and ethylbutyl-1,3-propanediol (molar ratio1:0.5:1), 41.4 g of dimethylolpropionic acid, 28.9 g oftrimethylolpropane monallyl [sic] ether and 330.9 g of methyl ethylketone, contained in a 6 1 reaction vessel fitted with a stirrer, areflux condenser and two feed vessels.

The reaction mixture is then heated to a temperature of 80° C. in anatmosphere of nitrogen. When the NCO content reaches 2.1%, 67.4 g oftrimethylolpropane are added to the reaction mixture.

A mixture of 320.6 g of n-butyl acrylate, 362 g of methyl methacrylate,76.7 g of hydroxypropyl methacrylate and 27.3 g of acrylic acid is thenadded over 3 hours at a reaction temperature of 82° C. At the same time186.4 g of a 12 percent solution of 2,2'-azobis-(methylbutyronitrile) inmethyl ethyl ketone is metered in over 3.5 hours.

After a further 2.5 hours at 105° C., 50.9 g of dimethylethanolamine and3480.2 g of deionized water are added.

After removal of the methyl isobutyl ketone [sic] in vacuo, a 30 percentaqueous dispersion which is free from coagulate and has a pH of 7.9 andan average particle diameter of 70 nm is obtained.

2. Preparation of Basecoats According to the Invention

Basecoat 1

200 g of binder dispersion A are predispersed with 59 g of water, 40 gof butyl diglycol and 256 g of a white pigment (titanium oxide) in adissolver for 15 min. at 21 m/sec. and is then ground for 30 min. in abead mill at 50° C. max.

A further 200 g of the above binder dispersion A, 55 g of a commercialmelamine resin and 66 g of demineralized water are added with stirringto 619 g of the above mill base.

Basecoats 2 and 3

A procedure similar to that used for the preparation of basecoat 1 isused. Further details are listed in Table 1.

                  TABLE 1                                                         ______________________________________                                                         Basecoat 2                                                                            Basecoat 3                                           ______________________________________                                        Binder dispersion B                                                                              300.00 g  --                                               Binder dispersion C                                                                              --        560.0 g                                          Water-soluble polyester 1)                                                                       80.0 g    --                                               Surfactant 2)      4.0 g     4.0 g                                            White pigment      --        256.0 g                                          Carbon black       30.0 g    --                                               Butyl diglycol     40.0 g    50.0 g                                           Melamine-formaldehyde resin 3)                                                                   60.0 g    58.0 g                                           Demineralized water                                                                              486.0 g   72.0 g                                           ______________________________________                                         1) Polyester having a number average molecular weight of 1900 and an acid     value of 30, based on neopentyl glycol, isophthalic acid, trimellitic         anhydride (molar ratio 2:1:0.75) (60% solution in butanol/water 1:1).         2) 50% solution of surfactant S (commercial product from Air Products) in     butyl glycol.                                                                 3) Luwipal 072, commercial product from BASF AG.                         

1) Polyester having a number average molecular weight of 1900 and anacid value of 30, based on neopentyl glycol, isophthalic acid,trimellitic anhydride (molar ratio 2:1:0.75) (60% solution inbutanol/water 1:1).

2) 50% solution of surfactant S (commercial product from Air Products)in butyl glycol.

3) Luwipal 072, commercial product from BASF AG.

3. Production of Basecoat/Clearcoat Finishes Using the BasecoatsAccording to the Invention

The basecoats according to the invention are applied by electrostaticspraying to zinc phosphated automotive body panels coated with acommercial electro-deposition primer and a commercial body filler insuch a way that paint films with dry film thicknesses (depending onshade) of 12 to 30 μm are obtained. After a brief flash-off period thecoating is recoated with a commercial clearcoat and baked for 30 minutesat 130° C. A panel painted in this way is once more coated with thebasecoat according to the invention, followed, after a brief flash-offperiod, by a commercial two-component refinish and dried for 30 minutesat 90° C. The dry film thicknesses of the clearcoats are about 40 μm.Finishes with good flow-out, high brilliance and very good mechanicalproperties are obtained.

After 240 hours' exposure to the constant humidity test according to SKDIN 50017 the coated panels show no changes on the surface of the paint.An adhesion test performed subsequently according to DIN 53 151 producesthe value 0. A blasting test carried out with 1,000 g of beveled shot(4-5 mm diameter) performed subsequently in an Erichsen stone impacter508 according to VDA only resulted in minute chipping.

We claim:
 1. A process for the production of a multicoat finish on a substrate surface, in which(1) a pigmented aqueous basecoat is applied to the substrate surface, (2) a polymer film is formed from the composition applied in stage (1), (3) a transparent topcoat is applied to the basecoat obtained in this way and subsequently (4) the basecoat is baked together with the topcoat, wherein the basecoat comprises as binder a polymer which can be obtained by polymerizing in an organic solvent or in a mixture of organic solvents(A) ethylenically unsaturated monomers or a mixture of ethylenically unsaturated monomers in the presence of (B) a polyurethane resin which has a number average molecular weight of 200 to 30,000, preferably of 1,000 to 5,000, and which contains on a statistical average 0.05 to 1.1, preferably 0.2 to 0.9, particularly preferably 0.3 to 0.7 polymerizable double bonds per molecule, and converting the reaction product obtained in this way to an anionically stabilized aqueous dispersion.
 2. The process as claimed in claim 1 wherein the polymer prepared from (A) and (B) has an acid value of 5 to 200, preferably of 10 to 40, particularly preferably of 15 to 30, a hydroxyl value of 0 to 100, preferably of 20 to 80, and a number average molecular weight of 2,000 to 20,000, preferably of 5,000 to 12,000.
 3. The process as claimed in claim 1 wherein the polymer prepared from (A) and (B) has a molecular wight distribution Q=M_(w) :M_(n) of 5 to 90, preferably of 10 to
 30. 4. The process as claimed in claim 1 wherein the polymer can be obtained by using the components (A) and (B) in a weight ration of 1:10 to 10:1, preferably 1:2 to 2:1, particularly preferably 1:1.
 5. The process as claimed in claim 1 wherein the polyurethane resin which contains polymerizable double bonds, introduced into the molecules of the polyurethane resin by incorporation of compounds which contain, in addition to a polymerizable double bond, at least two groups reactive toward NCO groups, is used as the component (B).
 6. The process as claimed in claim 1 wherein the polyurethane resin which contains allyl ether groups as polymerizable double bonds is used as the component (B).
 7. The process as claimed in claim 1 wherein the polyurethane resin which has trimethylolpropane monoallyl ether incorporated is used as the component (B).
 8. The process as claimed in claim 1 wherein the polymer can be obtained by using as the component (B) a polyurethane resin which has an acid value of 0 to 2.0.
 9. An aqueous paint which contains as binder a polymer which can be obtained by polymerizing in an organic solvent or in a mixture of organic solvents(A) ethylenically unsaturated monomers or a mixture of ethylenically unsaturated monomers in the presence of (B) a polyurethane resin which has a number average molecular weight of 200 to 30,000, preferably of 1,000 to 5,000, and which contains on statistical average 0.05 to 1.1, preferably 0.2 to 0.9, particularly preferably 0.3 to 0.7 polymerizable double bonds per moleculeand converting the reaction product obtained in this way to an anionically stabilized aqueous dispersion.
 10. The paint as claimed in claim 9, wherein the polymer prepared from (A) and (B) has an acid value of 5 to 200, preferably of 10 to 40, particularly preferably of 15 to 30, a hydroxyl value of 0 to 100, preferably of 20 to 80, and a number average molecular weight of 2,000 to 20,000, preferably of 5,000 to 12,000.
 11. The paint as claimed in claim 9 wherein the polymer prepared from (A) and (B) has a molecular weight distribution Q=M_(W) :M_(n) of 5 to 90, preferably of 10 to
 30. 12. The paint as claimed in claim 9 wherein the polymer can be obtained by using the components (A) and (B) in a weight ratio of 1:10 to 10:1, preferably 1:2 to 2:1, particularly preferably 1:1.
 13. The paint as claimed in claim 9, wherein a polyurethane resin which contains polymerizable double bonds, introduced into the molecules of the polyurethane resin by incorporation of compounds which contains, in addition to a polymerizable double bond, at least two groups reactive toward NCO groups, is used as the component (B).
 14. The paint as claimed in claim 9 wherein the polyurethane resin which contains allyl ether groups as polymerizable double bonds is used as the component (B).
 15. The paint as claimed in claim 9 wherein the polyurethane resin which has trimethylolpropane monoallyl ether incorporated is used as the component (B).
 16. The paint as claimed in claim 9 wherein the polymer can be obtained by using as the component (B) a polyurethane resin which has an acid value of 0 to 2.0. 